Infections with RSV are one of the major causes of viral lower respiratory tract illness in vulnerable infants and children. A vaccine against RSV remains unavailable despite numerous efforts over the past four decades. So far, only immunoprophylaxis with a monoclonal antibody against the RSV F protein can provide some protection for individuals at risk. The development of a vaccine that induces active protective immunity has been hampered by the risk for a severe lung disease following vaccination of numerous vaccine candidates. Protection against RSV could be achieved with an efficient vaccination strategy that induces neutralizing humoral immunity and a Th1-dominant cellular response without predisposing to enhanced lung disease. Based on the knowledge that (1) adenovirus gene transfer vectors (Ad) can evoke robust systemic and mucosal immunity against immunogens displayed on Ad capsid proteins, (2) Ad has potent adjuvants properties, and (3) Ad can also deliver neutralizing antibody genes expressed as transgenes, this proposal focuses on the development of a vaccine against RSV using modified Ad vectors. The commonly used human Ad5-based vectors have so far not been successful as human vaccine, partly due the high prevalence of anti-Ad5 immunity in humans. Non- human primate serotype AdC7 based vaccines have shown promise to induce long lasting protective mucosal and systemic immunity against respiratory pathogens, even in the presence of Ad5 immunity. This application will develop a novel AdC7-based RSV vaccine strategy that combines genetic delivery of an RSV neutralizing antibody gene to provide rapid and short term protection with active immunization by an RSV epitope expressed in the Ad capsid to provide long term protection. In aim 1 we will assess protective short-term immunity provided by mucosal genetic delivery of an anti-RSV neutralizing antibody expressed by an AdC7-based vector in neonatal mice. In aim 2 we will assess protective anti-RSV immunity by RSV F epitopes displayed in the AdC7 fiber protein with simultaneous genetic delivery of anti- RSV neutralizing antibody, with particular focus on the risk for developing enhanced RSV lung disease.